Purpose: Magnetic Resonance Spectroscopy (MRS) can assess fat unsaturation in human adipose tissue by measuring olefinic to methylene peak area ratios. Long echo time (TE) MRS techniques were optimized (considering J-coupling evolution and Tâ‚‚ relaxation) for such measurements in tibial bone marrow at 3T. The objective of this work is to compare apparent (to indicate inclusion of J-coupling effects) Tâ‚‚ relaxation times of olefinic and methylene resonances in breast and tibial bone marrow at 3T to determine if previously optimized long-TE values for bone marrow can be applied to breast.
Methods: Spectra were acquired from breast and tibial bone marrow of 4 female volunteers using a 3T whole body MRI scanner and a Point RESolved Spectroscopy sequence, with varying TE values and repetition time of 3 s. Apparent methylene and olefinic resonance Tâ‚‚ relaxation times were calculated for each volunteer. The ratios of Tâ‚‚ relaxation times in breast to tibial bone marrow were computed for each resonance. A mean and standard deviation were calculated over the volunteers.
Results: Average apparent Tâ‚‚ relaxation times were 83 Â± 7 ms and 90 Â± 4 ms (methylene resonance) and 36 Â± 2 ms and 40 Â± 5 ms (olefinic resonance) in breast and tibia, respectively. The average ratios (with standard deviations) of apparent Tâ‚‚ relaxation times in the breast versus tibial bone marrow were 0.91 Â± 0.12 (olefinic resonance) and 0.93 Â± 0.11 (methylene resonance).
Conclusion: Apparent olefinic and methylene Tâ‚‚ relaxation times are about 8 % lower in breast versus tibial bone marrow. Because breast Tâ‚‚ values differ from those in tibial bone marrow by a similar amount, comparisons between olefinic to methylene ratios in breast and tibial bone marrow can be made without Tâ‚‚ compensation. Thus, the previously optimized long-TE values are also adequate for olefinic to methylene measurements in breast.